I would caution you one thing, I cannot get my E8400 perfectly stable even at 3.6Ghz on my XFX 780i and it's not temps for either the NB or Core that I'm aware of. Besides that, the above mentioned xigmatek cooler, or the Cooler Master Hyper TX2 would be very nice coolers, I'm using the TX2 at the moment and never go above 60 even when I've tried my clocks at 3.6 and 3.825.
You know I don't know if that's true. I've seen my friends O/C their e8400 to 4.0GHz+. And thanks for the cooler information.